Varady, who co-wrote the 2013 bestseller The Every-Other-Day Diet: The Diet That Lets You Eat All You Want (Half the Time) and Keep the Weight Off, advocates a six-hour eating window. The 18-hour fast that follows results in many more clinical benefits and better weight loss compared to an eight-hour, or 10-hour window, she says.
Hong Kong nutritionist Michelle Lau, founder of nutrition consultancy Nutrilicious, explains the fundamentals of fasting’s benefits.
The cover of Varady’s book.
“Short-term fasting induces a cellular repair process called autophagy. Cells use old and unneeded cellular material and proteins for energy, and that, in turn, may lead to protection against neurodegenerative conditions and cancer,” Lau says.
The key is the length of the fast, and to induce autophagy requires low liver glycogen, which is usually only achieved after about 14 to 16 hours of fasting, possibly longer. That is why Lau urges anyone considering fasting to speak with a doctor or dietitian first.
The New England Journal of Medicine’s review outlined many of the proven benefits of fasting. Experts weigh in on four of them, described below.
The cover of Jeannette Hyde’s new book.
1. Weight loss
Jeannette Hyde is a UK-based nutritional therapist and author of The Gut Makeover. She has just published The 10-Hour Diet, in which she describes the weight-loss benefits of intermittent fasting as “gentle”, about 3.5kg shed over three months.
“This is thought to happen as people have to finish eating earlier in the evening so they aren’t consuming the usual calories from snacks on the sofa after dinner. Also, food eaten earlier in the day is burned up more than calories eaten late at night,” Hyde says.
“When people wake up in the morning and stretch the fast from 12 to 14 hours, they burn fat in this window by pushing breakfast back a bit and starting their day’s eating later.” She advocates a 14-hour fast, eating from 8am to 6pm, or 10am to 8pm, say.
Paul Jefcoate, a researcher in chronobiology and nutrition metabolism at the University of Surrey in the UK, agrees there might be a temptation to “cram” in calories during the feeding window, but says “this simplified approach to feeding-fasting” does seem to lead to eating fewer calories. The biggest plus to eating this way, Jefcoate says, is that no foods are off the menu – though it still requires a sensible approach to eating.
In overweight men and women, he says, time restricted feeding has been “shown to reduce appetite and increase fat loss”.
Paul Jefcoate, a researcher in chronobiology and nutrition metabolism at the University of Surrey in the UK. Photo: Twitter / @Paul_Nutrition
2. Lower blood pressure
A recent study from Baylor College of Medicine in Texas indicates that fasting reshapes the gut microbiota and that in turn lowers blood pressure.
Hyde says that research shows that within “just three months of practising 14-hour overnight fasting, and eating no later than 8pm, subjects’ blood pressure went back into normal range. It is thought to be a result of eating in the day when our bodies are designed to, rather than eating late at night, which we’re not designed to.
“Eating late can put a lot of strain on our digestive system and other organs such as the heart due to our circadian rhythm – the natural times that functions in the body happen.”
Joëlle Touchette Bradford, a naturopathic doctor at the Integrated Medicine Institute in Hong Kong. Intermittent fasting gives the body time to heal, she says. Photo: Winson Wong
She adds: “When we give the body a rest from digesting, by fasting overnight, the body goes into repair mode, autophagy, where cells are repaired and old ones are slung out.”
3. Reduced inflammation
Joëlle Touchette Bradford, a naturopathic doctor at the Integrated Medicine Institute in Hong Kong, says we shouldn’t consider fasting as starving but as giving the body time to heal.
If you are really bloated, for example, just fasting for 20 hours is enough to get back to a state of optimal digestion, she says. And it presents the opportunity for the body “to focus on calming down any inflammation, process any food that remains in the system and healing any minor wounds”.
With a reduction in inflammation comes faster cell turnover – thanks to that autophagy, described as an important detoxification function in the body to clean out damaged cells.
Anthea Smith’s intermittent fasting regime allows her the freedom to enjoy the food and drinks she likes on non-fasting days. Photo: Anthea Smith
Touchette Bradford says a break in eating allows for ‘cellular pruning’. “It gives the body a chance to heal and rid itself of cellular rubbish which can slow repair and even cause us to age faster.”
4. Better sleep
The theory is that intermittent fasting may help to regulate our circadian rhythm which determines sleep patterns. A well regulated circadian rhythm means you’ll fall asleep easily and wake up feeling refreshed, according to research published in 2018 in Nature and Science of Sleep.
If you stop eating before sunset, you’re encouraging your body’s natural sleep pattern by “circadian fasting”.
When you go to bed on an empty or almost empty stomach, the internal clocks in your digestive system sync with the ones in your brain; you’re switching off the internal lights before you switch off the external ones.